Vehicle drivetrain systems typically include a transmission having an output shaft connected through an elongated drive shaft to an input shaft of an axle assembly. Because of constraints imposed by the overall design of the vehicle, these shafts are rarely aligned such that their axes of rotation are co-axial. To accommodate this, and further to permit a small amount of relative movement to occur between the transmission and the axle assembly resulting from flexing of the vehicle frame during use, universal joints are usually provided in two locations: between the transmission output shaft and the forward end of the driveshaft assembly; and between the rearward end of the driveshaft assembly and the axle assembly input shaft. The universal joints permit the axes of rotation of the adjacent shafts to be angularly aligned, while providing a rotational driving connection between the adjacent shafts.
Generally, the universal joints used in driveshaft assemblies are Cardan type universal joints. A typical Cardan type universal joint includes a pair of yokes which are interconnected by a cross. The cross includes a central body portion having four cylindrical trunnions extending outwardly therefrom. The trunnions are oriented in a single plane and extend at right angles relative to one another. A hollow cylindrical bearing cup having a closed end is mounted on the end of each of the trunnions. A plurality of bearings, such as roller bearings or needle bearings, are provided between the outer cylindrical surface of a given trunnion and the inner cylindrical surface of the associated bearing cup to permit relative rotational movement therebetween. To form a Cardan type universal joint, a first yoke is connected to a first opposed pair of the bearing cups of the cross, while a second yoke is connected to a second opposed pair of the bearing cups. In the context of a driveshaft assembly, therefore, the first universal joint includes a first yoke secured to the end of the transmission output shaft and connected to the bearing cups mounted on the first opposed pair of the trunnions. The bearing cups mounted on the second opposed pair of the trunnions are connected by a second yoke for rotation with the driveshaft assembly. Similarly, the second universal joint of the driveshaft assembly includes a first yoke secured to the end of the second driveshaft member and connected to the bearing cups mounted on the first opposed pair of the trunnions. The bearing cups mounted on the second opposed pair of the trunnions are connected by a second yoke for rotation with the driveshaft assembly.
It is known that whenever a Cardan type universal joint is operated while the rotational axes of the two yokes are not aligned, non-uniform motion is developed. In other words, when one yoke (the driving yoke) is rotated an incremental angular distance, the other yoke (the driven yoke) may not rotate the same incremental angular distance. Rather, the driven yoke rotates either more or less than the incremental angular distance, depending upon the initial angular orientation. Similarly, when the driving yoke is rotated at a constant rotational velocity, the driven yoke does not rotate at the same constant rotational velocity. Rather, the driven yoke rotates either faster or slower than the rotational velocity, again depending upon the initial angular orientation. It has been found that the incremental angular displacement and velocity of the driven yoke vary in a sinusoidal manner relative to the constant angular displacement and velocity of the driven yoke.
The consequence of these sinusoidal variations in angular displacement and velocity in a vehicle driveshaft system is that undesirable torsional vibrations may be generated in the driveshaft assembly. These torsional vibrations can be somewhat annoying to a driver of the vehicle and, therefore, are undesirable. Also, these vibrations can in some cases damage various components of the vehicle. The magnitude of these torsional vibrations is proportional to the square of the operating angle of the universal joint. Where multiple universal joints are connected in series, the effects of universal joints may be combined and expressed as a single equivalent operating angle. Thus, the magnitude of the torsional vibrations in a multiple universal joint system is proportional to the square of the equivalent operating angle of the system.
To a certain extent, the torsional vibrations in a multiple universal joint system can be minimized if the two universal joints connected to the driveshaft assembly are properly oriented relative to one another. This is often referred to as phasing the driveshaft. The relative angular orientation of the yokes which are secured to the two ends of the driveshaft assembly is referred to as the phase angle. For example, let it be assumed that the inboard yokes of the two universal joints are aligned with one another (i.e., the axes of rotation defined by the respective pairs of cross bores formed through the associated yoke arms are parallel). This arrangement is referred to as a zero phase angle between the two universal joints. Further, let it be assumed that the plane defined by the first outboard yoke and the driveshaft is common with the plane defined by the second outboard yoke and the driveshaft. Finally, let it be assumed that the outboard yokes extend at operating angles relative to the driveshaft which are equal and opposite to one another. In this instance, the equivalent operating angle of the system is zero because the torsional vibrations generated by the first universal joint are equal and opposite (i.e., 180.degree. out of phase) to the torsional vibrations generated by the second universal joint. As a result, the torsional vibrations generated by the first universal joint are substantially canceled by the equal and opposite torsional vibrations generated by the second universal joint.
Unfortunately, the design of the vehicle in which the driveshaft assembly is installed dictates the directions in which the outboard yokes extend from the driveshaft assembly. Frequently, the outboard yokes do not extend in a common plane or at angles which are equal and opposite to one another. On the contrary, it is common not only that the two outboard yokes extend in different planes, but also that they extend at different operating angles. To accommodate this structure, while still providing some mutual cancellation of the undesired torsional vibrations, it is known to orient the two inboard yokes of the two universal joints at a non-zero phase angle (i.e., the axes defined by the respective pairs of cross bores are not parallel). This angular misalignment provides, in many instances, sufficient mutual cancellation of the sinusoidal variations to eliminate or otherwise reduce the annoying and/or problematic torsional vibrations during normal use.
To provide additional pliability for vehicle driveshaft assemblies to accommodate the flexing of the vehicle frame during operation of the vehicle, vehicle driveshaft assemblies are frequently provided with splined slip joint connections, which are cooperating male and female splined telescoping driveshaft members. The yoke shaft component of the driveshaft assembly is provided with external splines and the spline sleeve component of the driveshaft assembly is hollow with internal splines. The interengagement of the external and internal splines provides a positive rotational connection for the transmission of torque through the driveshaft. At the same time, the slip joint connection enables the yoke spline sleeve driveshaft assembly components to move axially with respect to each other to reconcile distance variations between the transmission and the axle assembly occurring during normal flexing of the vehicle frame.
One of the problems encountered during the manufacture and assembly of slip joint driveshafts is that it is difficult to accurately fix or establish the desired phase alignment between the yoke shaft and the spline sleeve driveshaft components. Care must be taken to assure that the external and internal splines of the yoke shaft and spline sleeve, respectively, are interengaged in the desired phase alignment, as specified by the manufacturer. In a typical driveshaft slip joint spline configuration anywhere from about 3 to about 75 splines are used on the yoke shaft, with an equal number of splines on the spline sleeve. Therefore, each phase angle rotation from one spline to the next results an a variation of anywhere from about 4.8 to about 120 degrees between the axes of the two end yokes.
While great pains are usually taken to properly phase align the driveshaft yoke shaft with the driveshaft spline sleeve, improperly aligned driveshafts are still inadvertently produced, requiring reassembly at additional labor expense. Typically, the insertion of the yoke shaft into the spline sleeve is carried out during a "blind" assembly procedure in which the operator cannot physically see the alignment of the splines. Further, after assembly, each driveshaft must be checked as to whether or not the phase angle between the yoke shaft and the spline sleeve has been properly set. It would be advantageous if a method and apparatus could be devised to facilitate accurate alignment of the yoke shaft and spline sleeve driveshaft components. Such an improved method and apparatus should not only increase the accuracy of the phase alignment of the two driveshaft components, but should also speed up the alignment process.
Another problem which has been encountered in the design and manufacture of vehicle driveshafts is that it is sometimes difficult to interpret what the desired phase angle relationship is from drawings that have been generated to illustrate the structure of the driveshaft assembly. In some instances, the standards used by a vehicle manufacturer may be different from the standards used by the supplier of the driveshaft. In other instances, the standards used by the designer of the driveshaft assembly may be different from the manufacturer of the driveshaft. Because of these difficulties, it would be desirable to provide a fixture which clearly and unambiguously identifies the phase angle relationships between the universal joints secured to the ends of a driveshaft.